1. Field of the Invention
The present invention relates in general to earth-boring bits, particularly to those having rotatable cutters in which seal assemblies retain lubricant within the bearing areas.
2. Background Information
One of the most successful seal means used in earth-boring bits of the type having rotatable cutters is the O-ring seal disclosed in commonly assigned U.S. Pat. No. 3,397,928, to Galle. The o-ring seal successfully confines lubricant to the bearing area while excluding detritus for long periods of time before failure.
A more recent seal development is the rigid or metal face seal. In the rigid face seal type, the seal interface is between one or two rigid, usually steel, seal rings. One or two elastomer o-rings serve to energize or urge the seal faces of the rigid ring or rings in contact with each other. The rigid face seal has proved to be as successful as the o-ring seal and provides an improved ability to accommodate pressure fluctuations in the bit lubricant.
A somewhat less successful design is the Belleville seal, in which elastomer elements are bonded to a rigid metallic ring or washer, which is placed under compression in the seal gland and the elastomer elements perform the bulk of the sealing.
Liquid drilling fluid is normally used for oil and gas well drilling, whereas compressed air is used as the drilling fluid in mining operations. Drilling fluid conveys cuttings to the surface and cools the bit. When the solid matter in drilling fluid is carried into the seal gland, it adheres to gland and/or seal component surfaces and causes deformation and/or slippage of elastomeric seal components. Moreover, these particles can accelerate abrasive wear of all seal components.
A need exists for seal assemblies that supplement the main bearing seal by assisting in the prevention of entry of debris into the seal assembly itself.
The exposure of cuttings to the mud of non-rotating parts is reduced. Only a small portion of the stationary ring of a metal face seal is exposed to the drilling fluid entering the seal gland. All of the other exposed components of the seal assembly are rotating with the cone.
A bit is provided having at least one leg extending downwardly and inwardly from the bit body. A cutter cone is rotatably mounted on a shaft extending inwardly from the lower portion of each leg. The annular space defined by the base of the shaft and the inner surface at the base of the cone forms a seal gland. An elastomeric o-ring sealingly engages an inner surface of the cone and a first rigid ring which rotates with the o-ring and cone. The o-ring energizes the first rigid ring for sealingly engaging a second rigid ring mounted to the leg of the bit near the base of the shaft. The second rigid ring is secured to and seals against a surface at the base of the shaft and is held stationary relative to the surface. A lubricant passage for lubricating the seal is pressurized by the drilling fluid pressure in the center of the bit body.